Automatic circuit interrupter



ll8- 19, 1952 H. o. sToELTxNG Er Al. 2,607,869

AUTOMATIC CIRCUIT INTERRUPTER 2 SHEETS-SHEET l Filed Sept. 8, 1951 RH 0www uw M WSW@ c m I0 o. a m M. M an. f r r 0 0 nl A A/Aa/ 3. Z ma o l xn S. l 2 -LNI l 0/n r s l .L .vv .L HeuY F RB m D f unwma aannu 4.

Allg- 19, 1952 H. o. sToELTlNG ET AL 2,507,869

AUTOMATIC CIRCUIT INTERRUPTER 2 SHEETS-SHEET 2 Filed Sept. 8, 1951INVNTOR7 Herman a 'Zoellinj lssell 1li/200;

QM Ffm' Patented Aug. 19, 1952 UNITED STATES PATENT GFFICE AUTOMATICCIRCUIT INTERRUPTER corporation of Delaware Application September 8,1951, 'Serial No. 245,704

' 7 Claims. 1

-This invention relates to an 4automatic circuit interrupting device forprotective `apparatus in electric transmission lines. v

Lightning arresters of the class hereinafter described comprise acombined enclosed arc gap and valve material connected in series. Thegap is intended to break down when a voltage higher than a predeterminedvalue is impressed thereon and to interrupt current now across the gapwhen the voltage and current flow have dropped to predetermined values.The valve `material is intended to limit current flow across the gap toan amount determined by the voltage impressed on Athe gap. Thus the gapand valve material are 3o-ordinated to permit voltages in an electricline in excess of a Vpredetermined value to be discharged to ground andto interrupt the flow of current to ground when the line voltages havereturned to a value below the predetermined value.

`Heretofore5 it has been the practice to provide circuit interruptersfor lightning arresters as described above, and which are so arrangedthat for ordinary discharges, the interrupter will not function, but forunusually heavy discharges which result from a breaking down of thevalve material, for instance, the interrupter will function andpermanently open the circuit to the ground of the lightning arrester.This type of structure vis shown in the patentto R. Earle, No.2,315,320granted March 30, 1943 for Automatic Circuit-InterruptingDevicaowned by the assignee ofthe present invention.

It is an object of this invention to provide a novel circuit interrupterwhich responds in its various embodiments to a materially reducedimpulse ratio; the impulse `ratio being defined as the ratio of thebreakdown voltageunder asta-ndard surge test wave front to the breakdownvoltage under normal-frequency voltage. y n

It. is another object of this invention to provide an yinterruptingdevice for lightning ,arresters with a pre-ionizing means for reducingits impulse ratio; the pre-ionizing means taking the form, in thepreferred embodiment, of a taperedv rially lowered by the use oi aceramic or other` high-dielectric-constant body as a spark initiator,

and which also provides a more consistent spark' with the novel circuitinterrupter attached with parts broken away and parts in section.

Fig. 2 is a fragmentary sectional view, substantially enlarged,illustrating the novel interrupter in its preferred embodiment. n

Figs. 3 through 6 are fragmentary sectional views, substantiallyenlarged, illustrating various modifications of the novel circuitinterrupter.

Referring to the drawings, it will be seen that the lightning arrestercomprises a `ceramic or other insulating casing l, within the upper partof which is housed the conductors 2 lwhich are spaced apart to form aseries of spark gaps 3. The upper part of the lightning arrester isconnected to the line wire or power line by means of the conductor l andis capped by means of the insulating cap 5. is provided with a lowerterminal S, and the negativeiresistance material 'l isinterposedrbetween thelower end of the spark gap structure and the lowerterminal E in accordance with the disclosure Vin the above mentionedpatent granted to R. H. Earle.

n The interrupting devicehas the general characteristics of thestructure disclosed in the priorv patent hereinabove mentioned, and iscomposed of an upper terminal indicated by the reference character 8 anda lower terminal indicated by the reference character E. The lowerterminal is provided with a shell-like portion I0 which carries anexplosive charge in the form of a cartridge Il. The shell it is spacedfrom a surrounding lip l2 of the upper terminal and is arranged toy beheated when heavy ksparking occurs and thereby ignite and causeexplosion of the explosive during the flow of excessive current from thelightning arrester throughthe interrupter. he two terminals are held inspaced relation by means of an insulating breakable shell I3 and theground wire 25S is electrically connected to the lower terminal, suchground wire being grounded as shown in Fig. l.

The upper terminal 8 may be provided with a threaded stem l5r whichscrews into the lower terminal 6 oi the lightning arrester, the lowerterminal 9 being connected to the ground wire'l-ll IThe lower part ofthe arrester by means of a screw I6, a suitable insulating shell I1provided for this connection.

In the preferred form of this invention illustrated in Figs. .1 and 2,the improved interrupter includes a novel insulating plug 2lis which maybe made preferably of steatite or other insulating material having arelatively high dielectric constant. The plug 20 rests in the bore 2l ofthe upper terminal 8. Laboratory tests have indicated that it ispreferable to have the plug positioned directly above the cartridge I Iwith. a minute air gap 22 therebetween, although satisfactory resultshave been obtained with the modified structures shown in Figs. 3 and 4,the plug` lightly contacting the upper surface of the cartridge II.

The plug is preferably provided with a well 23, the surface of which hasa conducting coating 24. It is within the scope of this invention to useany liquid conducting medium such as mercury, conducting ink, conductingpaint, or the like. Electrical contact between the well surface and theupper terminal 8 may be provided as shown with a cat Whisker biasedtowards Contact with one end formed in a coil spring 26. The free end ofthe insulating plug 20 is preferably tapered as shown to provide asubstantially conical discharge surface 21. A simple way of positioninga plug within the bore 2l of the upper terminal is to construct the plugwith an angular groove 28, in which is positioned a spring washer 29biased outwardly. The plug 20 may then be locked in position onengagement with the spring washer 29 and an annular groove 30 in theupper terminal.

Modifications of the novel structure and within the scope of thisinvention will now be described, the various components being identifiedby the same reference characters where they are substantially identical.Certain of the modified structures have insulating plugs in intimatecontact with the upper surface of the explosive cartridge While otherembodiments of the plug member provide a minute air gap, but it is to benoted that in all cases the plug is immediately adjacent the cartridge.

Fig. 3 illustrates a comparatively simple form of this invention. Here,the plug 35 is devoid of anylocking means such as the cooperating springwasher and annular grooves of the embodiment shown in Fig. 2. In thisembodiment, the plug is permitted to rest lightly upon the upper surface36 of the explosive cartridge II. This embodiment provides satisfactoryresults and is simpler to manufacture than the preferred embodiment.

Fig. 4 also discloses an embodiment of this invention utilizing aninsulating plug 31 resting on the upper surface 36 of the cartridge II.In this embodiment the plug 31 does not have the exposed end tapered,but employs two conducting coatings 38 and 39. The coating 38 in theWell portion 40 is substantially identical to that of the preferredrembodiment, while the coating 39 may be cup-like, as shown, extendingslightly upwardly from the base.

The embodiment illustrated by Fig. utilizes an air gap 22 between theplug 4U and the upper surface 36 of the cartridge II. Here the plugpreferably has an outer coating 4I of conducting material providingintimate electrical contact with the upper terminal 8. However, it willbe apparent that if close tolerances are maintained between the plug andthe terminal, the coating may be omitted. Here, the plug is providedwith a bore 42 defining an annular projecting wall 43.

Fig. 6 illustrates an insulating plug 44 similar to the preferredstructure of Figs. l and 2, but with the tapering omitted. Here, theexposed surface 45 is flattened on a plane substantially parallel to theplane of the upper surface 36 of the cartridge.

Operation of the improved circuit interrupter is as follows: Y

Referring to Fig. 2, which has been enlarged for convenient explanatorypurposes, the insulating plug 20 is. shown positioned to provide aminute air gap 22 between the discharge end and the upper surface 36 ofthe cartridge II.

It has been found in the practice of this invention that spark-overoccurs at lower values when a dielectric gradient is produced in theproximity of the terminals 8 and 9. This gradient is established betweenthe air as a dielectric and the relatively high-dielectric-constantinsulating plug. The dielectric flux lines established prior tospark-over are bent or refracted as they pass from one dielectric to theother of a different permitivity. The novel plug 20 is preferably formedas shown, with the free end tapered to provide a conical surface 21 as aconvenient means for focusing the refracted flux lines 46. Theconcentration of refracted flux lines readily serves to pre-ionize theatmosphere in the vicinity of the discharge surface 21 and the uppersurface 36 of the explosive cartridge.

A more precise control of the air breakdown is obtained by the use of aninsulating plug of arelatively high dielectric-constant which gives thedesired low impulse ratio by utilizing the radiation present in theusual enclosed gap. Obviously, the novel insulating plug serves only asa spark-over initiator. After breakdown has been initiated, current flowwill be established in the more favorable path between the upperterminal 8 and the conducting shell 41 of the cartridge. 'Ihis is showndiagrammatically by the lines 48 in Fig. 2. The insulating plug will beby-passed after initial breakdown with the current taking the easierpath 48, and heating the cartridge I I to cause it to explode, thussevering the ground connection from the lightning arrester.

The operation of the various modifications disclosed in Figs. 3 through6 is based on the same principle underlying the operation of thepreferred embodiment described above in connection with Figs. 1 and 2;viz, spark-over occurs at lower values when a dielectric gradient isproduced in the proximity of the opposed terminals 8 and 9.

The dielectric flux lines 46 of the embodiment illustrated in Fig. 3 areconcentrated by the focusing tapered surface providing discharge surface21. A satisfactory air breakdown occurs at the fringe areas designatedby the reference character 49. This breakdown is not as easilycontrolled as that of the minute air gap 22 provided in the preferredstructure. After the initial breakdown occurs, spark-over takes placebetween the upper terminal 8 and the shell 41 of y the cartridge II, thecartridge exploding upon heating to interrupt ground connection.

The Fig. 4 structure operates by setting up a concentration ofdielectric flux lines 46 between the conducting coating $8 and thecup-like coating 39 as shown.

The structure shown in Fig. 5 provides a means of concentrating iiuxlines 4S by utilizing an annular wall 43 projecting from the bore 42 ofthe upper terminal 8, to the air gap 22 between the exposed end of theplug 40 and the upper surface 36 of the cartridge,

Fig. 6 illustrates a further modification of the preferred structure ofFigs. l and 2. An air gap 22 is required here to insure a refracting ofthe iiux lines 46 because of theomission of the tapered dischargesurface of the preferred structure. Again, the ilux lines 46 produce abreakdown in the air gap 22, from which spark-over 'between the upperterminal 8 and the shell 41 occurs. In al1 embodiments it will beapparent that the insulating plug acts only as a means of concentratingdielectric flux lines for initiating spark-over. After spark-overoccurs, the insulating plug will be by-passed with the current takingthe easier spark-over path to ground.

We claim:

l. A circuit interrupter including a pair of terminals, an insulatinghousing embracing said terminals and holding them in releasable spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, and an insulating plug member in said bore and havingone end adjacent said cartridge.

2. A circuit interrupter including a pair of terminals, a frangibleinsulating housing embracing said terminals and holding them in spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, and an insulating plug member in said bore having oneend tapered and adjacent said cartridge.

3. A circuit interrupter including a pair of terminals a frangibleinsulating housing embracing said terminals and holding them in spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, an insulating plug member in said bore having one endopen in said .bore and the other end closed and adjacent said cartridge,and a contactor in said bore engaged at one end with said one terminaland at the other end with said closed end of said plug member.

4. A circuit interrupter including a pair of terminals, an insulatinghousing embracing said terminals and holding them in releasablc spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, an hollow insulating plug member in said bore havingone end open in said bore and the other end closed, said closed endbeing tapered and adjacent said cartridge, and a contactor in said boreengaged at one end with one terminal and the other end with said closedend of said plug member.

5. A circuit interrupter including a pair of terminals, a frangibleinsulating housing embracing said terminals and holding them in spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, and an insulating plug member in said bore, said plugmember being provided with a locking means, said locking meanscooperating with said one terminal, said plug member jointly providingan air gap with said cartridge.

6. A circuit interrupter including a pair of terminals, an insulatinghousing embracing said terminals and holding them in releasable spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, an hollow insulating plug member in said bore havingone end open in said bore and the other end closed and adjacent saidcartridge, said hollow plug member having a conducting medium containedtherein, and a contactor including a biasing portion for maintainingelectrical contact between said conducting medium and said one terminal.

7. A circuit interrupter including a pair of terminals, an insulatinghousing embracing said terminals and holding them in releasable spacedrelation, one of said terminals having a centrally located boreinteriorly of said housing, an explosive cartridge including a metalcasing secured to the other terminal within said housing and adjacentsaid one terminal, an hollow insulating plug member in said bore havingone end open in said bore and the other end closed, said hollow plugmember having a conducting medium contained therein, and a contactorincluding a biasing portion for maintaining electrical contact betweensaid conducting medium and said one terminal, and a locking meansarranged to jointly cooperate with said plug member and said oneterminal said plug member jointly providing an air gap with saidcartridge.

HERMAN O. STOELTING. RUSSELL A. WOOD.

No references cited.

